The present invention relates to a method and to a machine for making a continuous rod of the type wherein a web of wrapping material (e.g., cigarette paper) confines a rod-like filler of smokable material, particularly tobacco. A typical example of such product is a continuous cigarette rod which is produced in a cigarette rod making machine and is subdivided into sections (plain cigarettes) of unit length or multiple unit length.
A cigarette rod is obtained by converting a shower of tobacco particles (and/or particles consisting of other fibrous smokable material) into a stream containing tobacco in excess of that which is required in the rod, by trimming or equalizing the stream including removing the excess of fibrous material, and by thereupon draping the resulting rod-like filler into a web of cigarette paper or other suitable wrapping material. The draping normally takes place simultaneously with radial compacting of tobacco during transport through the compacting mechanism (garniture) which converts a flat web or strip of wrapping material into a tubular envelope surrounding the filler and having a seam extending in parallelism with the axis of the rod. It is also known to regulate the rate of removal tobacco by the equalizing device in response to signals which are furnished by a density monitoring device and denote the density of the filler, normally of the filler which is already confined in the wrapping material. The rate of removal of excess tobacco from the stream is regulated by changing the distance between the cutting element or elements of the equalizing device and the conveyor which transports the stream past the equalizing station.
The manufacturers of cigarettes strive to turn out cigarettes each of which contains a predetermined quantity of tobacco per unit length of the article. This is desirable on several grounds, especially in order to avoid the introduction of excessive quantities of expensive ingredient (tobacco) into the individual articles. The presently preferred technique involves the use of a monitoring device (e.g., a beta ray detector which employs a source of corpuscular radiation and an ionization chamber or another suitable transducer) which is placed adjacent to the path of the cigarette rod and furnishes signals denoting the monitored density of succesive increments of the advancing cigarette rod. The signals are utilized to effect adjustments of the equalizing device with reference to the aforementioned conveyor, i.e., to change the distance between the cutting plane and the conveyor and hence the height of the filler.
Prior to the invention and development of satisfactory monitoring devices which can ascertain the density of successive increments of a rapidly moving stream or filler consisting of tobacco and/or other fibrous smokable material and can transmit signals to a motor which is designed to instantaneously change the position of the equalizing device with reference to the conveyor for the tobacco stream, the cigarette making machines were devoid of equalizing means. In such antique machines, the tobacco stream was condensed by conveying it, at a gradually decreasing speed, through a tunnel wherein the stream was confined at all sides. Such compacting was to compensate for the inability of the cigarette making or analogous machine to immediately form a tobacco stream whose density is uniform and invariably matches or closely approaches an optimum value. The aforementioned reduction in the speed of forward movement of the tobacco stream was intended to reduce the dimensions of cavities between neighboring tobacco particles in the stream and to thus reduce the extent of deviation of density of the tobacco stream from an optimum value. Reference may be had, for example, to U.S. Pat. No. 2,671,452. It will be readily apparent that such rudimentary mode of reducing the extent to which the density of tobacco filler in a cigarette rod deviates from an optimum density is far from satisfactory and, therefore, all modern cigarette rod making and like machines are equipped with adjustable equalizing devices, with density monitoring devices, and with means for adjusting the equalizing devices when the monitored density deviates from an optimum value. Such devices and such adjusting means are standard components of all presently produced cigarette rod making machines.
The ability of a modern cigarette rod making machine to turn out cigarettes whose actual weight matches the prescribed weight is one of the criteria which are given foremost consideration by the purchasers of such machines. This stands to reason because a modern cigarette rod making machine, which can turn out in excess of 7000 cigarettes per minute, can save large sums of money if the actual weight of cigarettes which are produced therein matches the prescribed minimum acceptable weight.
Another criterion which is determinative of the quality and hence of the sales appeal of a modern cigarette rod making machine is its ability to turn out relatively hard or firm rod-shaped smoker's products. As a rule, a smoker will be unable to ascertain the exact quantity of tobacco in a cigarette. Instead, the smoker will judge the cigarette by ascertaining its firmness which is done by squeezing the cigarette between two fingers to thus determine the resistance which the filler offers to radial compacting. It is already known to ascertain the firmness of the fillers of cigarettes and to regulate the rate of removal of excess tobacco from the tobacco stream in dependency on deviation of the monitored firmness from an optimum or desirable firmness. Reference may be had to U.S. Pat. No. 3,411,513 which discloses a method and an apparatus for gauging and controlling firmness in cigarettes and the like.
It will be noted that all heretofore known proposals to regulate the weight or mass and the firmness of cigarettes involve an adjustment of the trimming or equalizing device with reference to the adjacent conveyor for the tobacco stream. The regulation of weight was considered more important and, therefore, the presently known cigarette rod making machines employ means for monitoring the density of cigarettes and means for adjusting the position of the equalizing device in response to signals which are furnished by such density monitoring means so that the position of the equalizing device is changed when the monitored density deviates from the optimum density. Attempts to regulate the firmness of cigarettes presently involve the provision of means for changing the firmness of tobacco particles, i.e., for influencing the characteristics of tobacco particles in the course of the so-called primary treatment which involves processing of tobacco prior to introduction into the magazine of a cigarette rod making machine. Such proposals involve so-called puffing of tobacco ribs and analogous treatment of tobacco particles ahead of the cigarette making station.